It is known that increased generation of oxidants and (or) reduced endogenous antioxidant defense mechanisms are associated with the etiology of diabetic vascular complications. Although a close correlation exists between increased oxidative stress and the activation of matrix metalloproteinases (MMPs), little is known about the effect of hyperglycemia on the regulation and contribution of MMPs in the vascular system. Therefore, we aimed to examine whether omega-3E (50 mg/kg per day for 4 weeks), a long-chain (n-3) polyunsaturated fatty acid enriched with vitamin E, has a beneficial effect on vascular dysfunction via affecting MMPs in streptozotocin-diabetic rat aorta. Omega-3E treatment improved the diabetes-induced impairment of phenylephrine-induced contraction and isoproterenol-induced relaxation responses of aorta. It also exhibited marked protection against diabetes-induced degenerative changes in smooth muscle cell morphology. Biochemical data showed that this treatment significantly prevented important changes, such as inhibition of MMP-2 and MMP-9 activity, loss of tissue inhibitor of matrix metalloproteinase-4 (TIMP-4) protein, increase in tissue levels of thiol oxidation, endothelin-1, protein kinase C (PKC), and cAMP production, and decrease in tissue level of nitrite. These results indicated that omega-3E significantly improved impaired vascular responses and regulated the activity of MMPs via preventing oxidative injury. Overall, the data suggest that omega-3E ameliorates or prevents vascular reactivity alterations in diabetes. Such an observation provides preliminary evidence for omega-3E's potential as a therapeutic agent for the prevention of vascular disorders in diabetes.